The present invention relates generally to an aqueous polymer dispersion and a coating composition made thereof, especially to a “green” antibacterial polymer dispersion with improved color stability property upon exposure to heat and/or light, and the coating composition made thereof.
Inorganic microbiocides on which metal ions are supported frequently exhibit instabilities which cause them to discolor upon exposure to heat or sun light. Hence, these inorganic microbiocides frequently cause aqueous binder emulsion and coating compositions into which they are incorporated to undergo conspicuous changes in coloration. Accordingly, the use of these microbiocides is effectively limited to systems for which such conspicuous changes in coloration can be tolerated.
U.S. Pat. No. 7,390,774 discloses a light stable antimicrobial composition comprising a metal complexed with a polymer containing 1-vinylimidazole as monomer, wherein the metal is selected from copper, silver, gold, tin, zinc and combinations thereof. The antimicrobial composition exhibits better light stable property than the conventional inorganic microbiocides consisting of metal ions supported by materials including active carbon, apatite, zeolite, and various phosphates. However, a higher level of color stability is still desired. Moreover, the antimicrobial composition comprising a metal complexed with a polymer needs some kind of organic solvent and ammonia to help incorporation, which increases the total volatile organic compound (VOC) content of the coating composition and causes bad odor. Low VOC and ammonia free are also desired.
The problem addressed by the present invention is to find an improved aqueous antibacterial polymer dispersion which shows lower discoloration of the corresponding formulations upon exposure to heat and/or sun light as compared to the antimicrobial composition of the U.S. Pat. No. 7,390,774. Moreover, the present invention also provides an antibacterial polymer dispersion comprising a metal complex with a polymer that is stripped by steam to reduce the VOC for low VOC and low odor request.